This invention relates to the storage of high-level wastes for an extended period of time. More specifically, this invention relates to an improvement in the method for the storage of high-level radioactive wastes as solids in metal canisters by making the canisters self-sealing.
A problem facing the nuclear industry which has received much attention is how to dispose of radioactive wastes so that they will never contaminate the biosphere with radioactivity. While disposal of these wastes in a form and in an environment in which no contamination of the biosphere is possible under any conceivable circumstances for the entire period that radioactivity is at a dangerous level is the ultimate objective of waste management engineers, no such disposal procedure has as yet gained wide acceptance. As an alternative or supplement to ultimate disposal, an engineered storage employing buildings, vaults, tanks, etc. which will require continuous surveillance and maintenance for up to 100 years may be employed.
A number of factors must be considered in the development of these storage methods which are to last for 100 years. For example, integrity of the storage container, cost of solidifying the wastes, retrievability of the wastes if necessary for reprocessing and cost of storage must all be considered.
Large volumes of liquid waste have been and are being stored in large tanks. Due to the tremendous cost of storing liquids, considerable effort has gone into programs for developing methods for solidifying these wastes for longterm storage. For example, the use of cement for the fixation of radioactive wastes has been studied extensively, and from a production standpoint, is probably the most convenient way in which to solidify waste. All that is required is that the material to be solidified be mixed with water and the mixture cast into the desired monolithic shape and allowed to set. However, some radioactive salts are readily leachable from concrete and the retrievability of the radioactive material from the concrete may pose some future problems.
Studies are also being conducted into methods for solidifying the liquid wastes by calcining them in a fluidized-bed or batch-type pot calciner or transforming the wastes into glass. In either case, the calcine or glass would then be sealed into metal canisters for storage. Because of the heat developed by the radioactive waste, the canisters must be cooled, either by air or by storage in a water-filled tank. In either environment, the canister is subject to failure of its integrity which may result in the release of radioactive material to the environment.